1. Field of Invention
This invention relates to a method and composition for inhibiting corrosion of a variety of metals and, in particular, to the inclusion of corrosion inhibitors and shelf life extenders in plastic sheet material useful for packaging of metal products.
2. Brief Statement of the Prior Art
The protection of metal surfaces with corrosion inhibitors has traditionally been achieved by applications of coatings of the corrosion inhibitors to the surfaces to be protected. This technique has shortcomings; it contaminates the metal surfaces, and many metal objects, such as delicate scientific instruments, can not be protected in this fashion.
Some limited success has been achieved in packaging metal objects in plastic film in which the corrosion inhibitor is incorporated in the film. These techniques have found only limited acceptance, however, since difficulties have been experienced when attempting to incorporate corrosion inhibitors in plastic and no single plastic film product has been developed which effectively inhibits corrosion of a wide variety of metals. Additionally, the plastic film containing the corrosion inhibitors has a limited shelf life since corrosion inhibitors must be used which have sufficient volatility to effect transferring to the metal surfaces after packaging, and the corrosion inhibitor is ultimately lost from the plastic film.
The attempts to incorporate the corrosion inhibitors in plastic films have used pellets of molding resin in which the corrosion inhibitors have been incorporated as the resin for the extrusion of the plastic film and sheet. The storing and handling of the pellets in which the corrosion inhibitors have been incorporated generates fines and dust and this dust presents inhalation toxicity problems to the workers as most corrosion inhibitors are potentially toxic. Also this technique requires a significant amount of cleaning and preparation of equipment, particularly since most of these corrosion inhibitors have specific activity for a limited number of metals and frequent changing of the molding resin is required.
Accordingly, there exists a need for a simple method to incorporate corrosion inhibitors in plastic sheet and film during extrusion. For this purpose a corrosion inhibitor concentrate should be supplied to the extrusion equipment as a stable liquid gel which can be metered into the plastic during the extrusion operation, thereby avoiding the potential inhalation toxicity problems as well as greatly simplifying the manufacturing technique. Additionally, a need exist for extending the shelf life of products packaged in the plastic film containing the corrosion inhibitors and for providing a single product which exhibits corrosion inhibition of a wide variety of metals including ferrous metals, aluminum and its alloys, copper and its alloys and magnesium base alloys.